Time warp activation signal provider, audio signal encoder, method for providing a time warp activation signal, method for encoding an audio signal and computer programs

Abstract

An audio encoder has a window function controller, a windower, a time warper with a final quality check functionality, a time/frequency converter, a TNS stage or a quantizer encoder, the window function controller, the time warper, the TNS stage or an additional noise filling analyzer are controlled by signal analysis results obtained by a time warp analyzer or a signal classifier. Furthermore, a decoder applies a noise filling operation using a manipulated noise filling estimate depending on a harmonic or speech characteristic of the audio signal.

The invention claimed is:   
     
       1. Audio encoder for generating an audio signal, comprising:
 a controllable time warper for time warping the audio signal to acquire a time warped audio signal; 
 a time/frequency converter for converting at least a portion of the time warped audio signal into a spectral representation; 
 a temporal noise shaping stage for performing a prediction filtering over frequency of the spectral representation in accordance with a temporal noise shaping control instruction, wherein the prediction filtering is not performed, when the temporal noise shaping control instruction does not exist; 
 a temporal noise shaping controller for generating the temporal noise shaping control instruction based on the spectral representation, 
 wherein the temporal noise shaping controller is configured for increasing a likelihood for performing the predictive filtering over frequency, when the spectral representation is based on a time warped audio signal or for decreasing the likelihood for performing the prediction filtering over frequency, when the spectral representation is not based on a time warped audio signal; and 
 a processor for further processing an output of the temporal noise shaping stage to acquire the encoded audio signal; 
 wherein the temporal noise shaping controller is configured for estimating a gain in a bitrate or a quality, when the audio signal is subjected to the prediction filtering by the temporal noise shaping stage, for comparing the estimated gain to a decision threshold, and 
 for deciding, in favor of the prediction filtering, when the estimated gain is in a predetermined relation to the decision threshold, 
 wherein the temporal noise shaping controller is furthermore configured for varying the decision threshold so that, for the same estimated gain, the prediction filtering is activated, when the spectral representation is based on a time warped signal, and is not activated, when the spectral representation is not based on a time-warped audio signal. 
 
     
     
       2. Audio encoder in accordance with  claim 1 , in which the time warper comprises a signal classifier for detecting voiced or unvoiced speech, and
 in which the temporal noise shaping controller is configured for increasing the likelihood, when a voiced speech is detected, or when an unvoiced speech is detected and the spectral representation is based on the time warped audio signal. 
 
     
     
       3. Method for generating an audio signal, comprising:
 for time warping the audio signal to acquire a time warped audio signal; 
 converting at least a portion of the time warped audio signal into a spectral representation; 
 performing a prediction filtering over frequency of the spectral representation in accordance with a temporal noise shaping control instruction, wherein the prediction filtering is not performed, when the temporal noise shaping control instruction does not exist; 
 generating the temporal noise shaping control instruction based on the spectral representation, 
 wherein a likelihood for performing the predictive filtering over frequency is increased, when the spectral representation is based on a time warped audio signal or wherein the likelihood for performing the prediction filtering over frequency is decreased, when the spectral representation is not based on a non-time-warped audio signal; and 
 processing an output of the temporal noise shaping stage to acquire the encoded audio signal; 
 wherein a gain in a bitrate or a quality, when the audio signal is subjected to the prediction filtering by the temporal noise shaping stage, is estimated, and 
 wherein the estimated gain is compared to a decision threshold, for deciding, in favor of the prediction filtering, when the estimated gain is in a predetermined relation to the decision threshold, 
 wherein the decision threshold is varied so that, for the same estimated gain, the prediction filtering is activated, when the spectral representation is based on a time warped signal, and is not activated, when the spectral representation is not based on a time-warped audio signal. 
 
     
     
       4. A non-transitory computer-readable storage medium having program code stored thereon, wherein the program code, when executed by a computer, performs the method of  claim 3 .